A stent is an elongated device used to support an intraluminal wall. In the case of a stenosis, a stent provides an unobstructed conduit for blood in the area of the stenosis. Such a stent may also have a prosthetic graft layer of fabric or covering lining the inside or outside thereof, such a covered stent being commonly referred to in the art as an intraluminal prosthesis, an endoluminal or endovascular graft (EVG), or a stent-graft.
A prosthesis may be used, for example, to treat a vascular aneurysm by removing the pressure on a weakened part of an artery so as to reduce the risk of rupture. Typically, a prosthesis is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e. by so-called “minimally invasive techniques” in which the prosthesis, restrained in a radially compressed configuration by a sheath or catheter, is delivered by a deployment system or “introducer” to the site where it is required. The introducer may enter the body through the patient's skin, or by a “cut down” technique in which the entry blood vessel is exposed by minor surgical means. When the introducer has been threaded into the body lumen to the prosthesis deployment location, the introducer is manipulated to cause the prosthesis to be ejected from the surrounding sheath or catheter in which it is restrained (or alternatively the surrounding sheath or catheter is retracted from the prosthesis), whereupon the prosthesis expands to a predetermined diameter at the deployment location, and the introducer is withdrawn. Stent expansion may be effected by spring elasticity, balloon expansion, or by the self-expansion of a thermally or stress-induced return of a memory material to a pre-conditioned expanded configuration.
A vena cava filter is an implantable filter, typically implanted in a patient's inferior vena cava using minimally invasive techniques, for reducing the risk of arterial plaques dislodged during surgery or clots formed in the bloodstream from becoming lodged in and partially or completely blocking vessels supplying blood and oxygen to critical organs, such as the heart, lungs and brain. Such filters enable dangerous blood clots to be removed from circulation and held in a safe location until they can be dissolved by medication or extracted, again using minimally invasive techniques. Conventional implantable blood filters employing a variety of geometrics are known, but may are generally basket or cone shaped to provide adequate clot-trapping area while permitting sufficient blood flow. Also known are filters formed of various loops of wire, including some designed to partially deform the vessel wall in which they are implanted.
Typically, endoluminal devices such as vena cava filters and stents expand by one mechanism or another, not by some combination. That is, balloon expandable devices are not also self-expanding, and self-expanding devices are not typically balloon expandable. While it is known to “model” self-expanding stents to conform to anatomy in which the stent has been deployed to a shape suitable for accepting the stent, such modeling does not vary the diameter of the stent, but rather varies the anatomy. For example, a self-expanding stent deployed in an artery having a plaque deposit on the walls may be modeled to crush the plaque deposit down.
Self-expanding devices typically are known for excellent crush resistance, potential for longitudinal flexibility, for exerting a constant outward force to maintain an open vessel, and for having the capacity to elastically expand and contract with the blood vessel. On the other hand, self-expanding devices typically must be sized accurately to provide acceptable outward force and cannot generally be manipulated to a larger diameter after deployment. Self-expanding devices are typically made of a superelastic material, such as a superelastic grade of nitinol, which has a limited x-ray visibility.
Balloon-expandable devices are typically capable of expansion into a range of sizes, and typically are relatively stiff and inflexible. Balloon-expandable devices do not typically recover if crushed in the body, however, and are rigid bodies that do not expand and contract with motion of the vessel. Balloon-expandable devices are also typically longitudinally rigid, limiting delivery through tortuous anatomy. Balloon-expandable devices are made of a plastically deformable metal such as stainless steel, platinum, or a plastically deformable grade of nitinol.
In light of the advantages and disadvantages of self-expanding and balloon-expandable technologies as currently known, there is a need in the art for technology bridging the advantages of both.